Ken Phillips on the RHESSI "Fe Feature" (Joint with WG1)

  • Observations:
    - Never see evidence for FeXXII or lower
    - May 21, 1980 famous flare at peak shows no evidence even at FeII (or other) K-line
    - RHESSI Fe observations seem to have no counterpart in the earlier spectroscopic data
    - NEAR spectrum at 0.7 keV resolution from a PIN Si detector seems to show clear DEM effects. Also there are data from RESIK, now alas suffering from a power-supply problem

  • K-alpha nitty-gritty:
    - there is a pair of lines at 6.4 keV, in 1:2 ratio, almost certainly formed via fluorescence (radiative excitation of inner shell). One gets completely screened 2s-1p transitions.
    - Collisional excitation of K shell? Not likely - Limb darkening expected from absorption in spicules or whatever... One also has a time-variation signature which is a clinching argument in favor of fluorescence
    - Smeared Chianti spectra, Mazzotta ionization equilibria, show Fe-Ni mixture above 7.5 keV at v. high temperatures (e.g. > 20 MK). At 100 MK see v. strong FeXXVI complex plus many 8-9 keV line groups

  • Discussion: - Abundances? Meyer 1985; Feldman-Laming 2000; Fludra-Schmelz - FIP effect vagaries. Low FIP enhanced by 3-4 x photospheric in the corona? Mason-Young 1997 on spatial dependences of low/high FIP abundances - Is the Mazzotta revision of the ionization
    balances "revolutionary" or not? Nice plot compares Arnaud-Rothenflug with Mazzotta, showing main differences at lowest temperatures
    - What about the continuum? BCS spectra were not good for that.
    - Phillips-Neupert paper re direct collisional excitation (March 29 1980 huge spike event)
    - "The whole world is going towards Chianti..." and it is very useful stuff. Note that it will be adapted to kevocentric users soon, we hope. Meanwhile use ch_ss.pro
    Last modified: Tue Sep 23 13:05:14 BST 2003